This invention relates generally to vacuum apparatus and methods, and, more particularly, relates to apparatus and methods for generating a localized, noncontact vacuum seal between a vacuum apparatus and the surface of a workpiece.
A wide range of processes, for photolithography and repair of photomasks, integrated circuits, TV picture tubes, and liquid crystal display (LCD) structures, utilize focused beams such as electron beams, ion beams or laser beams. Conventional focused beam repair systems require that the workpiece be placed inside an evacuated chamber to reduce the number of atmospheric particles which scatter the beam and reduce resolution. In the case of electron beam or ion beam systems, evacuation is required because the electron gun itself must be in a region of very low pressure, on the order of 10.sup.-6 mmHg.
At the conclusion of the repair stage, the chamber is opened and the workpiece is removed. A new workpiece is inserted, and the cycle repeats. The requirement of repeatedly evacuating the chamber adds cost and complexity, and is time consuming, sharply reducing the throughput of focused beam repair systems.
It is known that a localized, non-contact vacuum seal can be created between an apparatus and a workpiece surface, using a series of differentially pumped apertures. The basis of differential pumping lies in the introduction of resistances in the path of gas flow between pumping stages. Large pressure ratios can be achieved if several such stages are used in succession. The mathematical basis for non-contact vacuum devices using differential pumping is described in E. Donath, "Differential Pumping of a Narrow Slot," Journal of Vacuum Science, incorporated herein by reference; and A. H. Shapiro, "Optimum Design of Pumping System for Maintaining Vacuum in a Chamber Open to the Atmosphere Through an Aperture," Vacuum, 1963, incorporated herein by reference.
The Donath publication discusses experimental results on differential pumping of a narrow rectangular slot open to the atmosphere at the inlet side, and the pumping requirements for achieving pressures on the order of 10.sup.-6 torr at the terminus of the slot.
The Shapiro publication discusses a vacuum system for allowing electron beam welding without a window separating the electron gun and the workpiece.
Differential pumping and localized vacuum seals are also disclosed in the following U.S. Pat. Nos.: 3,904,505, Aisenberg. 4,118,042, Booth. 4,524,261, Petric et al. 4,720,633, Nelson.
Aisenberg discloses apparatus for depositing a thin film upon a base substrate, the apparatus including a differentially pumped vacuum chamber.
Booth discloses an air bearing vacuum seal assembly including a two-stage differential pumping arrangement for maintaining a selected pressure gradient between a vacuum region and an air cushion region.
Petric et al discloses localized vacuum apparatus having elements for defining plural concentric vacuum chambers, including a central vacuum zone through which a particle beam is directed. Internal channels connect the vacuum chambers to individual vacuum pumps, and the chambers are differentially pumped to form a noncontact vacuum seal between the device and a workpiece.
Nelson discloses scanning electron microscope apparatus including an aperture column having a series of differentially pumped pressure zones.
Differentially pumped vacuum devices, however, are typically bulky in radial and axial dimension--i.e., in the dimensions perpendicular to and parallel to the beam, respectively--, and therefore cannot be utilized for processing near the edges of a semiconductor wafer or LCD structure.
Moreover, the construction of differentially pumped devices has heretofore required the assembly of numerous mechanical parts, thereby increasing cost and complicating the task of maintaining critical mechanical tolerances in the axial dimension. This dimension is especially important because it is determinative of the gap separating the workpiece surface and the workpiece-facing surface of the localized vacuum apparatus. If the gap is excessive, vacuum is reduced due to increased influx of atmospheric particles. An insufficient gap, conversely, increases the risk of contact with, and resultant damage to, the workpiece surface. Accordingly, tolerances in the axial dimension are critical in construction of localized vacuum apparatus.
Additionally, differentially pumped devices typical of the prior art provide no elements for delivering process gases for deposition on, or etching of, a substrate.
It is accordingly an object of the invention to provide localized vacuum apparatus and methods adapted for use with particle beam or laser beam apparatus, and which provide a high degree of isolation of the process zone from atmospheric particles.
It is another object of the invention to provide localized vacuum apparatus and methods which can achieve high vacuum levels in a central process zone.
It is a further object of the invention to provide localized vacuum apparatus which is compact in radial and axial dimensions, and which can be dynamically and controllably positioned, in three orthogonal axes, at selected positions over the workpiece surface.
It is another object of the invention to provide localized vacuum apparatus and methods for the introduction of selected process gases for providing selected reactions in the process zone.
It is yet another object of the invention to provide localized vacuum apparatus which is simple and inexpensive to construct with closely controlled mechanical tolerances.
Other general and specific objects of the invention will in part be obvious and will in part appear hereinafter.